A Jeep window regulator typically breaks due to worn or snapped cables, stripped gears in the regulator mechanism, a cracked plastic carrier that holds the window in its track, or a motor that overworks the regulator until something inside it fails. Age, frequent use, and a window that's already slightly misaligned all accelerate wear.
Most window regulators use a cable-and-pulley system or a scissor-style metal arm to raise and lower the glass smoothly inside the door. Over thousands of up-and-down cycles, the cables can fray and eventually snap, especially if the window has ever bound up or been forced past a slight obstruction. The small plastic clips and carriers that attach the regulator to the glass are another common failure point, since plastic becomes brittle with age and temperature fluctuations, and Ann Arbor's hot summers and freezing winters take a toll on them.
A regulator can also fail from the inside out. The gears that translate the motor's spinning motion into the up-and-down movement of the window are usually made of a mix of metal and plastic, and the plastic teeth in particular can strip or shear off after enough cycles, especially if the window ever gets stuck partway and the motor keeps trying to force it. Once a few teeth are gone, the regulator either slips without moving the glass or grinds and struggles before failing.
Where the failure happens can point to how it started. A cable that's frayed near a pulley usually means normal wear over time, while a sudden snap paired with a grinding or popping sound often points to something binding in the door, like a loose clip or debris in the track, that puts extra strain on the regulator until it gives out.
If your Jeep's window has started moving slowly, unevenly, or not at all, it's worth having the regulator checked before it fails and leaves the window stuck open or closed. Hoover Street Auto Repair in Ann Arbor can inspect the regulator, cables, and track to find out exactly what's wearing out.